Production of crude metal castings or finished metal castings usually involves the processes of melting, refining and casting. In these processes the molten metal comes into contact with the melting furnace, the molten metal vessel, the runner and the mold, which are built of non-metallic materials such as refractories. Thus it sometimes happens that the crude metal castings or finished metal castings contain non-metallic inclusions which orginate from the refractories. These non-metallic inclusions, which greatly hinder the working of the crude casting or injure the functions of the finished product, should be eliminated as far as possible. As stated above, however, the production process of crude metal castings or finished metal castings involves a number of sources for the non-metallic inclusions such as the linings of the melting furnace, the molten metal vessel, the runner and the mold, which are invariably built of refractories containing similar elements.
For this reason it is difficult to trace the sources of the non-metallic inclusions in the material or product, even through analysis. It is still more difficult to determine what refractories at the traced source make these inclusions.
Thus under the present circumstances no appropriate counter-measure can be immediately taken when non-metallic inclusions are found in the material or product.
For the purpose of locating the source of non-metallic inclusions contained in the material or product owing to the casting, a method of utilizing the radioisotope as the tracer has been tried in the laboratory. In the practical application of this method, however, it is extremely difficult to reliably shield the operator from the radiation of radioisotopes which have to be concentrated enough to enable the measurement, while the dispersion of used radioisotopes is unavoidable. It is for these reasons that the radioisotope method still fails to become practical.